Stop reading the arm64 domain when it's known
There is no need to read the domain on arm64 when there is only one
in the ACPI tables. This can also happen when the table is missing
as it is unneeded.
Reported by: dch
Sponsored by: The FreeBSD Foundation
(cherry picked from commit 0906563718d35643789fc2b3c4cf1fc6884755e5)